1. Technical Field of the Invention
The present invention relates to an apparatus for adjusting the position of an image reader unit on which a sensor such as a charge-coupled device (CCD) line sensor for image reading and a lens for projecting an original image on to the sensor are joined to each other in a specific positional relationship along the optical axis.
2. Description of Related Art
For controlling the relative position between a lens and a sensor and their orientations, it is generally necessary to provide five or six axes for adjustment. There have been some image reader units provided with adjusting mechanisms for manually or automatically controlling each axis for adjustment. FIG. 10 shows such six adjusting axes for positioning a lens 100 and a sensor 200.
In FIG. 10, x, y, z1, and z2 respectively represent the lengths of movement along the X, Y, and Z axes. Angles of rotation around the Y and Z axes are denoted respectively by ry and rz. The adjustment along x, y, z1, z2, and around ry and rz is made for the following purposes:
x: alignment of reading reference between the original document do and the sensor 200; PA1 y: alignment between focusing point of the lens 100 and pixel location of the sensor 200 for adjustment of reading position; PA1 z1: adjustment of distance between the lens 100 and the sensor 200 for magnification focusing; PA1 z2: adjustment of distance between the original document do and the image reader unit IRU on which the lens 100 and the sensor 200 are joined to each other in a specific positional relationship for adjusting major scanning magnification; PA1 ry: focusing of both center and edge of the original document for correction of defocusing at one end; PA1 rz1: adjustment of inclination of the sensor 200 with respect to a reference line for skew correction; and PA1 rz2: adjustment of inclination of the image reader unit IRU with respect to the reference line of the document do for skew correction.
Generally, the maximum reading width of the sensor 200 in the scanning direction is large enough to cover the entire size of the original document placed on a platen glass, thus eliminating the need for positional adjustment along the X axis. For example, if the reduction of the lens 100 is 1/9 and the sensor 200 has 5000 pixels (with the pitch of 7 micrometers), the reading width of the sensor 200 is 315 mm, which is greater than the width 297 mm of a landscape A4 sheet. Accordingly, the adjustment of the sensor 200 along the main scanning direction can be eliminated, thus enabling five-axis adjustment.
FIGS. 11 to 13 illustrate a conventional apparatus for adjustment of five axes. The lens 100 is fixedly mounted at a given position on a mounting platform 102 with a positioning guide 104 and a metal band 106. The sensor 200 is fixedly mounted to a sensor holder 202, which is connected to the mounting platform 102 by an intermediate support 220 so that the adjustment of z1, ry, and rz axes can be made. The mounting platform 102 is coupled to a base 108 of an image reading apparatus for adjustment of y and z2 axes.
More specifically, the adjustment of y is made by height control with a group of screws 230 between the mounting platform 102 and the base 108 shown in FIGS. 12 and 13. The adjustment of rz is accomplished by the relative movements between a sensor holder 202 and the intermediate support 220 about a screw 222 with the control of screws 224 and springs 225 as shown in FIGS. 11 and 12. The adjustment of z1 is made by the relative movements along the optical axis i between the intermediate support 220 and the mounting platform 102 with the control of screws 204 in slots 205 shown in FIG. 12. Similarly, the adjustment of z2 is made by the relative movements along the optical axis i between the mounting platform 102 and the base 108 with the control of screws 206 in slots 207. The adjustment of ry is accomplished by the relative movements about a screw 212 between the intermediate support 220 and the mounting platform 102 with the control of a screw 214 and a spring 215 as shown in FIGS. 11 to 13.
The positioning of the lens 100 and the sensor 200 is determined through movements and rotation according to an output voltage of the sensor 200 released on receipt of image information obtained by reading a test pattern on the original document do.
In the above-described conventional position adjusting mechanism, y is the only axis along which the lens 100 and the sensor 200 are unitedly adjusted. Since the adjustment of z1, z2, ry, and rz is made only for the sensor 200 separately of the lens 100, the lens 100 must initially be mounted with highly accurate positioning with respect to the z1, z2, ry, and rz axes. Also, the adjustment of y using the three screws 230 is troublesome and tends to cause inclination of the surface along the optical axis and the surface vertical thereto.
The sensor 200 is carried by the sensor holder 202 which has a center of rotation around the screw 222 as shown in FIGS. 12 and 13. The adjustment of rz is thus conducted around the screw 222 which is away from the optical axis i, across which the sensor 200 is located, by the distance y1 as best shown in FIG. 14A. When the angle of inclination of the sensor 200 is changed by the adjustment of rz as shown in FIG. 14B, the viewing level e relative to the unvarying optical axis i of the lens 100 is dislocated by the distance y2. In other words, the adjustment of rz affects the length of y, thus requiring readjustment of y after completion of the adjustment of rz.
Moreover, the screw 212 for the adjustment of ry is spaced by the distance z3 toward the lens side from the surface where the sensor 200 is mounted as shown in FIG. 12. Because of this, the adjustment of ry causes changes in image reading position of the sensor 200 along the Z axis. The adjustment of ry thus affects the lengths of z1 and z2, requiring readjustment of z1 and z2 after completion of the adjustment of ry.
Accordingly, the overall adjusting mechanism becomes intricate in construction and requires a considerable amount of operating skill. The adjustment of each axis must be repeatedly conducted so as to complete all of the adjustments of the axes interacting each other, thus increasing the duration of the overall adjusting operation.